1. Industrial Field of Application
The invention relates to a frame sequencing method for application in re-ordering decoded video picture sequence that consist of picture frame with and without bi-directional-predictive (B) coded frame in a more efficient and less costly means.
2. Related Art of the Invention
In encoding digital picture, frames in the picture sequence are usually classified as Intra frame (I frame), Predictive frame (P frame) and Bi-directionally-predictive frame (B frame). In I frame, the frame is coded without reference to any other picture. The P frame is coded using motion estimation and motion compensation from a previous I or P frame.
The B frame is coded using motion estimation and motion compensation from a previous and a future I or P frame. In the process of encoding, the digital picture is usually encoded into one of the following sequence:
1. I1 I2 I3 I4 . . . PA0 2. I1 P2 P3 P4 . . . PA0 3. I1 P2 B3 P4 B5 . . . PA0 4. I1 P2 B3 B4 P5 B6 B7 . . . PA0 1. I1 I2 I3 I4 . . . PA0 2. I1 P2 P3 P4 . . . PA0 3. I1 B3 P2 B5 P4 . . . PA0 4. I1 B3 B4 P2 B6 B7 P5 . . . PA0 1. Perform frame sequencing with fewer frame memory buffer. PA0 2. Re-order with shorter frame delay. PA0 1. The frame type of the incoming frame whether it is I, P frame or B frame. PA0 2. The location of B frame in the frame buffer. PA0 3. The previous read and write operation. PA0 1. Input sequence with no B frame PA0 2. Input sequence with B frame
After going through the decoding process, video data suitable for display on the TV monitor are generated. However, the output sequence from the decoder is still in the encoded sequence which is not suitable for display on the TV monitor except sequence 1 and sequence 2 mentioned above. The required display order is as follow for the above 4 sequences:
The most common method of performing the frame re-ordering is to provide 4 banks of frame memory buffer and perform the reordering after 3 frame delay. This method of re-ordering is shown in illustration 1 below for sequence 4 which is the most complicated sequence:
__________________________________________________________________________ Illustration 1: Reordering sequence for IBBPBBP . . . __________________________________________________________________________ 33 ms 33 ms 33 ms 33 ms 33 ms 33 ms ##STR1## ##STR2## ##STR3## ##STR4## ##STR5## ##STR6## Frame Buffer F1 WR I1 RD I1 WR P5 Frame Buffer F2 WR P2 Frame Buffer F3 WR B3 RD B3 WR B6 Frame Buffer F4 WR B4 RD B4 __________________________________________________________________________
In the above mentioned way of performing the frame reordering, two frame memories are dedicated to store the I frame and P frame where each frame memory stores one frame, and the other two frame memories are dedicated to store the B frame where each memory stores one frame. Because the frame memory are confined to store the video frame in a pre-defined manner, the logic required to design the frame sequencer for performing the frame re-ordering will be straight forward. Furthermore, with three frame delays, there will not be any frame lost.
However the prior art of frame-sequencing has some disadvantages. Firstly, four frames of memory buffer are required to perform the frame re-ordering, which is very costly. Secondly, there will be three frame delays before the required frame is scanned out and displayed on the TV monitor which is very inefficient. It is therefore desirable to derive a less costly and more efficient method to perform the frame-sequencing for the decoder.